The present invention relates generally to gas discharge devices, especially those utilized in ring laser angular rate sensors, and more particularly, to the block and cathode construction found in such assemblies.
Ring laser angular rate sensors are well known and are particularly described in U.S. Pat. No. 3,373,650, issued to Killpatrick, and U.S. Pat. No. 3,390,606, issued to Podgorski, both of which are assigned to the assignee of the present invention. The above referred to patents are incorporated herein by reference thereto.
Ring laser angular rate sensors of the type referred to utilize a block of material that is substantially stable, both thermally and mechanically. The block ususally includes a plurality of interconnected gas containing tunnels or passages which form a closed-loop path in the shape of a triangle, a rectangle, or any polygonal path. At each intersection of a pair of interconnected tunnels is a mirror mounted on the block. This arrangement of mirrors and interconnected tunnels forms an optical closed-loop path. Further, at least one anode and one cathode are each mounted on the block and in communication with the gas. Each of the components, including the mirrors, anode, and cathode, are sealed to the block to form a gas tight seal by any of a variety of techniques. The block is usually filled with a lasing gas such as a mixture of helium and neon. A sufficiently large electrical potential is applied between the anode and cathode to cause a discharge current therebetween which results in the production of a pair of counter-propagating laser beams within the block.
In some embodiments of ring laser angular rate sensors, a unitary body such as a quartz block, provides the gas discharge device including the optical closed-loop path. Such a system is shown in U.S. Pat. No. 3,390,606. Podgorski shows a unitary block, such as quartz or Cervit, comprised of a plurality of interconnected cavities or tunnels. Prior art ring laser angular rate sensors, like Podgorski, usually include at least one cathode and two anodes strategically positioned, usually symmetrically, along the optical closed-loop path. The pair of anodes and the cathode are electrically connected to a source of energy to produce a pair of electrical currents which flow in opposite directions along the optical closed-loop path. The current is established by the applied electrical potential between one cathode and one anode of sufficient magnitude to ionize the gas. As will be understood by those skilled in the art, a pair of anodes are symetrically placed along the closed-loop path of the laser beams so that gas flow effects caused by one of the electrical currents is balanced by gas flow effects caused by the other one of the electrical currents.
The performance of the cathode in ring laser angular rate sensors critically impacts the life of the sensor. In laser operation, the cathode attracts positive ions which bombard a generally metallic, electron emitting cathode surface, such as aluminum. The bombardment of the metallic cathode surface causes a sputtering effect which dislodges the electrically conductive material of the cathode surface. The sputtered material is attracted back to the cathode surface to create a metallic film thereon. As a consequence, the sputtered material tends to preferentially bury the neon gas between the cathode housing and sputtered film created thereon. This results in loss of the He-Ne gas from the cavity. A sufficient loss of lasing gas from the optical cavity results in the inability of the gas discharge device to operate resulting in the laser beams to cease lasing.
Present day research is directed to miniaturization of ring laser angular rate sensors. In such sensors, the optical path is a triangular or rectangular path where each path segment or side is in the order of one inch or less, and the thickness of the laser block is less than a one half inch. Accordingly, the laser block is relatively small compared with prior art laser blocks and contains a very limited amount of lasing gas. This latter fact, i.e. limited amounts of lasing gas, exacerbates the difficulty of achieving long life lasers.
Prior art cathode construction and gas laser techniques are described in U.S. Pat. No. 4,007,431, issued to Abbink, et al and U.S. Pat. No. 3,614,642, issued to Hochuli, et al. Also, such are described in a paper entitled, New Hollow Cathode Glow Discharge, by A. D. White, Journal of Applied Physics, Volume 30, No. 5, May, 1959, and a paper by Hochuli, et al, entitled, Cold Cathodes for Possible Use in 6328 Single Mode He-Ne Gas Lasers, A Review of Scientific Instruments, Volume 36, No. 10, October, 1965. Prior art cathodes as described in these and other patents and publications do not lend themselves to miniature lasers to achieve long life operation. This is so since the laser blocks are small and the sensor package needs to be kept small and of low weight.